Optical bus system and method

ABSTRACT

The invention relates to a bi-directional optical data transfer system. The data is transferred by a diffuse light between several electronic components with several transmission links, wherein each transmission link is provided with a covering to prevent the transmission links from interfering with each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system for the bidirectional opticaltransmission of information. In particular, it relates to the connectionof electronic components via a bidirectional optical bus system.

2. Description of the Related Art

Electronic systems are normally composed of a series of fixed and/orvariable electronic components (subsystems), which are connected to oneanother by a bus, which transports signals from one component toanother.

Thus digital computer systems for example are designed in this way. Anumber of individual cards or electronic components form subsystems,which are integrated into a bus system, which transports signals fordata, storage addresses, interrupts and the like. One of these cards maycarry a processor for the execution of application programs, whileothers in turn may contain controllers for workstations or displays,adapters for mass storage units or interfaces for LANs (Local AreaNetworks) etc. However, the subsystems can also comprise navigationunits, e.g. for use in cars, and video/audio or remote control units.

The functional electronic circuits on the individual cards or componentshave access to the common bus system for the transmission of data,addresses and control signals according to a certain bus protocol.

This type of packaging has important advantages. Thus a varying numberof different types of subsystems can be configured in the system as awhole, for example. Adaptation of the system to the respective userenvironment is simple and can often be undertaken by the user withoutfurther assistance. New functions and improved technology can beintegrated without difficulty at a later date without having to replacethe entire system. Furthermore, diagnosis and repair of the system areimproved by isolating individual subsystems.

Conventional hard-wired bus systems are relatively expensive and havedisadvantages. In so far as electronics technology is experiencingincreasing integration, connectors for transmitting signals from oneunit to another are becoming ever more expensive or reliability can onlybe achieved at a very high cost. Added to this is an ever greater spacerequirement

Some suggestions have been made for replacing parallel hard-wired(“copper”) backplane bus systems for connecting individual subsystems ofan electronic system, especially in the field of optical technologies.In spite of the necessity of converting electrical high-speed signalsinto optical signals and vice-versa, several optical backplane bussystems have been proposed. However, in this process optical signals arestill only transmitted from one special point to another special pointinside optical fibres. The biggest problem appears to lie in the factthat proposed optical bus systems, which could perhaps be used toconnect a large number of electronic components, are very much moreexpensive and are only to be made as reliable as the hard-wired bussystems they are intended to replace at considerable expense. Exoticoptical components, precise alignment within the components and the sizeof the optical units have caused the application of optical technologiesto fail in electronic systems in which a large number of components haveto communicate with one another via a common bus system.

It is also known to use light communications systems for serial and/orparallel communication, for example infrared systems in the case oflight distribution in open spaces with air as the medium (remotecontrols) or laser light systems via optical fibres.

However, these systems have the disadvantage that either mutualinterference restricts the application to so-called half-duplexoperation, signals only being able to be transmitted simultaneously inone direction (IR remote control), or optical fibres or glass-fibrecables are used, which are susceptible to faults, can only be renderedoperational using expensive plug-in systems and with regard to whichproblems occur in the transition of light between the cable and theplug-in connection (plug), for example due to condensation (laser lightsystems).

U.S. Pat. No. 5,113,403 and U.S. Pat. No. 5,209,866 disclose anelectronic system consisting of a number of subsystems or electroniccomponents, which are connected by an optical bus. The individualelectronic components are arranged in a housing in such a manner thatoptical interface units disposed on each component form a monoaxial,bidirectional optical bus working in free space which distributeselectrical signals among the individual components. These signals aretransmitted along a single linear axis as polarized light beams. Hereeach individual component has a bus interface unit for generatingoutgoing light beams and receiving incoming beams along both directionsof the axis respectively. The interface units use laser generators,photodetectors and amplitude-beam-splitters.

In spite of an improvement in the technique, however, these systems arestill cost-intensive and only allow for compact construction to a verylimited extent, since each individual component requires opticalinterface units.

Furthermore, these systems display lower reliability on account of thelarge number of optical elements used.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide a system forthe bidirectional optical transmission of information which utilizes,theadvantages of optical technologies on the one hand and is economical onthe other hand, displays a high degree of reliability in relation tofaults and also permits compact construction of the individualelectronic components.

This object is achieved according to the invention by a system for thebidirectional optical transmission of information with the aid ofdiffuse light between several electronic components with n transmissionlinks.

In the system according to the invention, sheathing is provided for atleast (n−1) transmission links in such a manner that mutual obstructionof the individual transmission links is prevented. In this regard asingle transmission link can be formed as a so-called “open transmissionlink”, i.e. this transmission link is not sheathed. Although the diffuselight conducted through this transmission link can then spread freely,the other transmission links are not influenced owing to theirsheathing.

The system according to the invention offers the advantage that theadvantages of an optical information transmission system, such as lowsusceptibility to faults, full-duplex operation and, in the case of amulti-channel execution, a real time application option can be utilizedoptimally by the use of economical receiver or transmitter devices. Withthe spread of diffuse light in free space, the problem normally existsthat without the use of expensive modulation processes, light can onlybe transmitted in one direction simultaneously without mutualinterference. This is acceptable for applications for which it issufficient to transmit the information content only slowly. However, forcertain requirements, for example an application in cars, this is notacceptable, as here a swift exchange of information with real-timecharacteristics is important. This disadvantage is remedied by thetransmission system according to the invention.

Infrared light (IR light) can be used as diffuse light, for example, butany other diffuse light is also suitable.

The use of IR light as an example of diffuse light makes it possible touse. Standard IrDA (Infrared Data Association) elements, such asinfrared receivers or transmitter units and to manage in this casewithout electrical connectors, optical coupler devices or complicatedoptical plug-in systems. Here no costly type of light modulation, suchas phase shift keying, frequency or polarization modulation isnecessary; the information is instead transmitted simply by the normalstates “light on” and “light off” (on-off keying). Known procedures canbe used as the transmission protocol.

A further advantage of using IR light consists in the fact that thesystem can operate as a genuine “real-time” system, i.e. only minimalconflict times occur (latency). Furthermore, a bus transfer is possiblewhich permits simultaneous access by several users to the bus system(simultaneous multi user access).

Since when using infrared light no electrical fields of any kind areproduced and the system is also insensitive to such fields, it is idealfor use in a sensitive environment. Furthermore, it is immune to shocks,vibrations and the respective surroundings. It thus has an extremely lowsusceptibility to faults in relation to condensation, dust, UV radiationetc.

The subsystems used can be any units communicating with one another, forexample processors, and also devices such as mobile telephones, TVs,navigation units or graphics units, audio/video units and remote controlsystems.

BRIEF DESCRIPTION OF THE DRAWINGS

The system according to the invention is described in greater detailbelow with reference to the drawings.

FIG. 1 shows a diagrammatic representation of the mode of operation ofthe transmission system according to the invention,

FIG. 2 shows-an enlarged representation of the transmission systemaccording to the invention with several transmission links arrangedadjacent to one another,

FIG. 3 shows a single electronic component as part of the transmissionsystem according to the invention,

FIG. 4 shows several electronic components arranged one behind anotherwithin the transmission system according to the invention; and

FIG. 5 shows a diagrammatic representation of the option of simultaneousaccess by several users to the transmission system according to theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

In the present example, the diffuse light used for optical transmissionof the information consists of IR light. However, any other diffuselight can be used, e.g. diffuse laser light, electroluminescence etc.The use of light in the infrared wavelength range (for example 870 nm)as the transmission medium has the advantage that relatively cheapstandard components, which are common in the consumer goods industry,such as IR diodes and possibly even photoresistors, can be used astransmitting or receiving devices. A simple transmission protocol isalso available in the IrDA physical layer protocol. When using othertransmitting and receiving devices, any other transmission protocol cannaturally be used. A further advantage of the use of IR light consistsin the fact that the system offers the best conditions for the creationof a “real-time system” due to the light transmission links separatedfrom one another. This includes inter alia the fact that informationwhich has a high priority also receives preferential access to certaintransmission links, while low-priority information is “diverted” toother transmission links. Furthermore, the transmission speed of lightis very high and in the application example is only dependent in anegligible way (10 cm corresponding roughly to 333 ps) on thetransmission length and loading of the bus system.

FIG. 1, represents diagrammatically the mode of operation of thetransmission system according to the invention. An electronic system 1communicates, for example, between its subsystems 3, 5 via an opticalbus 7. The bus transmits the relevant information in this process alongcertain transmission links from one subsystem to the other. If subsystem3, for example, wants to communicate information to subsystem 5,electrical signals 4 corresponding to the information to be transmittedare generated in an appropriate component of a processor unit (notshown). In the present example these signals consist of the sequence11101001. These signals are subsequently routed via a bus controller,which takes over conversion to the respective protocol, and then routedvia lines 6 to a conversion unit 8 such as a modulator/demodulator.

The signals are then routed via lines 9 in such a manner that the IRdiode 13 is turned on and off accordingly as a transmitter device. Here“1” in the signal sequence selected means “light on” and “0” means“light off”. The electrical signals are converted in this way into lightsignals 10 It should be pointed out that when using IrDA components,conversion has to take place to pulsating light owing to their ACcoupling, i.e. in the event of a sequence of several “1” signals, thediode is turned on and off again each time. If other components areused, the pulsing can possibly be dispensed with. In the presentexample, an amplifier (not shown) amplifying the signals is alsoconnected in series.

The pulsating light emitted by the IR diode 13 now radiates diffusely inall directions. As already indicated above, several transmission linksmay exist next to one another in the transmission system according tothe invention. To avoid mutual influencing of the transmitting andreceiving devices of these transmission links lying adjacent to oneanother, the radiated light is now routed, according to the inventionalong the transmission link provided (in the present example fromsubsystem 3 to subsystem 5) in a sheath 12. The transmitting andreceiving devices project into the sheath. This sheath 12 thus forms aclosed “channel” between the individual subsystems.

The diffuse light is now routed along the selected transmission linkpredetermined by the sheath 12 by reflection along the internal surfaceof the sheath 12 until it arrives at its destination, subsystem 5. Thereit meets the receiving device 14, which in the present example includesa photodiode 15 as a receiver However, other components are alsoconceivable correspondingly on the receiving side, such asphotoresistors etc, as the expert can easily recognize.

The received light signals 17 are now converted by the receiving device14 back into electrical signals 19 corresponding to the output signals 4and routed through the lines 16 to a conversion unit 18 such as amodulator/demodulator. The signals are then transmitted through thelines 20 to the bus controller 21 of the receiving electronic components5.

FIG. 2 shows an enlarged representation of the system with severalsheathed transmission links 12 arranged adjacent to one another. Eachindividual transmission link 12 can be used for the transmission ofindependent information along the double arrow shown in each direction.Due to the sheath according to the invention, the transmission links donot exert any mutual influence on one another. In a special form ofperformance of the system according to the invention, eight transmissionlinks are provided, so that a maximum of eight communication levels arepresent next to one another. However, any number of transmission linkscan be provided.

An “automatic gain control” devices (not shown) can be provided at thereceiving devices, which control devices re-amplify signals which havebecome attenuated by absorption on their way along the transmissionlink, or attenuate accordingly signals which are too strong.

In a particularly advantageous configuration of the invention, thesheath is an integral part of the housing 22 (FIG. 3), into which theelectronic components (subsystems) are embedded. In this way, the sheathcan be manufactured in the same working step as the housing. No“backplane infrastructure” is required either, i.e. no subsystems haveto be provided, as each further housing automatically extends the bus.

FIG. 3 shows a single component with the related transmitting andreceiving devices and the corresponding sheaths.

The sheath preferably has a light-reflective inner surface, so that thediffusely radiated light can be routed along the sheath. The innersurface is preferably porous, so that the diffuse light can be reflectedas randomly as possible in all directions.

In a particularly preferred form of performance, the sheath consists ofmagnesium, as magnesium has a very favourable ratio of weight tostability. However, it is also conceivable to use any other porous metalsurface or synthetic material as the sheath material.

The sole factor of importance is the feasibility of being able to routediffuse light along the inner wall of the sheath.

Since the diffuse light spreads in all directions, the form of sheath isnot restricted to straight channels. These channels can thus be routedin any form, for example bent or folded. However, it is advantageous toarrange various electronic components in a defined spatial arrangementone behind another, in order to avoid long paths and to save material.

FIG. 4 shows a spatial arrangement of this kind of several subsystemsone behind another. The individual components are each connected to oneanother via the sheathed channels 12. The advantages of an arrangementof this kind lie in the modular method of construction Only the numberof components required is arranged together in each case. A stationarysystem of this kind is therefore arbitrarily expandable Even componentswhich do not use the optical transmission system can be integrated intothis arrangement. However, at least one channel must then be present,which guarantees that the other transmission links are not influenced.In addition, this channel need not necessarily have transmitting and/orreceiving devices (transceivers).

Owing to the elimination of mutual interference of the transmissionlinks, it is possible by means of the transmission system according tothe invention to operate several communication levels adjacent to oneanother using diffuse light without interference. The option thereforeexists of actual simultaneity of communication While fully utilizing theadvantages of an optical system it is thus possible to achieve fullduplex operation, which permits multi-channel communicationsimultaneously on several communication levels.

In a further preferred form of performance, all the existingtransmission links are sheathed.

The consequence of this is that several users can access the same bussystem at the same time “Multiple simultaneous access” of this kind isshown in FIG. 5.

Thus, the transmission system according to the invention permitssimultaneous communication of subsystem A with the subsystems B and F,for example. It is possible for the subsystems C and E or D and F tocommunicate with one another at the same time as this communication.Information can be transmitted in parallel between the subsystems inthis way without any obstruction of the individual transmission linksoccurring. Arrangements can also be provided at the individualsubsystems that take over appropriate handling of the information forthe respective subsystem.

What is claimed is:
 1. System for bi-directional optical transmission ofinformation between a plurality of electronic components within ahousing by using a diffuse light, the system comprising n differenttransmission links between each two of the plurality of components, anda sheath that prevents mutual interference between the transmissionlinks for at least (n−1) transmission links, the sheath being anintegral part of the housing, wherein the n different transmission linksare arranged adjacent to one another and the information is transmittedby on-off keying.
 2. System in accordance with claim 1, wherein thediffuse light comprises IR light.
 3. System in accordance with claim 1,wherein the transmission links comprise one of a transmitting device anda receiving device.
 4. System in accordance with claim 3, wherein thetransmitting device comprises an IR diode.
 5. System in accordance withclaim 1, wherein the sheath includes a light-reflective inner surface.6. System in accordance with claim 5, wherein the inner surface isporous.
 7. System in accordance with claim 1, wherein the sheathcomprises magnesium.
 8. System in accordance with claim 1, wherein theelectronic components are in a defined spatial arrangement one behindanother and each of the electronic components are connected together bythe sheath.
 9. System in accordance with claim 1, wherein eighttransmission links are arranged one behind another.
 10. System inaccordance with claim 1, wherein all transmission links are sheathed.11. System in accordance with claim 3, wherein the receiving devicecomprises an IR diode.
 12. A method for bi-directional opticaltransmission of data between a plurality of electronic components havingn transmission links within a housing by using diffuse light, the methodcomprising: transmitting data using on-off keying, wherein individualones of said plurality of electronic components are arranged one behindthe other and connected by a sheathed channel that is an integral partof the housing.
 13. System in accordance with claim 1, wherein thesystem is used in an optical bus system for electronic systems.
 14. Themethod in accordance with claim 12, wherein the transmission of the datais for an optical bus system for electronic systems.
 15. The method inaccordance with claim 12, wherein each of said transmission linkscomprises a diode and said on-off keying comprises turning on said diodeand turning off said diode.
 16. The method in accordance with claim 12,wherein said sheathed channel forms a closed channel between saidindividual ones of said plurality of electronic components.
 17. Themethod in accordance with claim 12, wherein said individual ones of saidplurality of electronic components project into an interior of saidsheathed channel.
 18. A system for bi-directional transmission ofinformation between a plurality of electronic components by usingdiffuse light, the system comprising: a housing; n differenttransmission links provided between two of the plurality of electroniccomponents, the transmission links being arranged adjacent to oneanother; and a plurality of sheaths that prevent mutual interferencebetween the transmission links, wherein the plurality of sheaths are anintegral part of the housing.
 19. The system of claim 18, wherein theelectronic components are located within said housing.
 20. The system ofclaim 18, wherein the information is transmitted by on-off keying. 21.The system of claim 18, wherein the transmission links comprise an IRdiode.
 22. The system of claim 18, wherein the diffuse light comprisesIR light.
 23. The system of claim 18, wherein each of the sheathsincludes a light-reflective inner surface.
 24. The system of claim 23,wherein the inner surface is porous.
 25. The system of claim 18, whereineach of the sheaths comprises magnesium.
 26. The system of claim 18,wherein the electronic components are in a defined spatial arrangementone behind another and each of the electronic components are connectedtogether by the plurality of sheaths.
 27. The system of claim 18,wherein eight transmission links are arranged one behind another. 28.The system of claim 18, wherein all transmission links are sheathed. 29.A system for bi-directional optical transmission of information betweena first and second component by using a diffuse light, the systemcomprising: a housing; n different transmission links between said firstand second component, and a sheath that prevents mutual interferencebetween the transmission links, said sheath being an integral part ofthe housing.
 30. A system as claimed in claim 29, wherein the ndifferent transmission rinks are arranged adjacent to one another.